SIMO power converters are promising candidates for power management integrated circuits (PMICs) because only one inductor is used to supply multiple outputs quasi simultaneously. One case of such SIMO converter type is the SIDO converter, the single inductor dual output type. The present invention may be practiced with a plurality of DC-DC power converter designs, such as—but not limited to—at least one of a group including multi-output DC-DC up (boost) converters, multi-output DC-DC down (buck) converters, multi-output DC-DC up/down (buck-boost) converters, multi-output DC-DC inverting converters, multi-output DC-DC converters with positive and negative output, and multi-output DC-DC up/down converters with multiple positive and negative outputs. Limitations in the chosen number of outputs will occur depending on performance requirements such as load regulation, or maximum load and un-balance range of loads throughout the various outputs.
Usually, the system current limit is the sum of the individual output currents. One topic of interest is the handling of output overload situations, i.e. situations in which the sum of the currents drawn from the outputs of the SIMO power converter exceeds the system current limit. In prior art systems, such output overload situations cause the severe voltage drops not only at the output of the SIMO power converter which is actually overloaded. In a SIDO power converter, for instance, both output voltages at both outputs may drop significantly although only one output is overloaded. As a consequence, also operation of the supplied device at the non-overloaded output of the SIDO may be interrupted as long as the overload condition persists. This problem is caused by regulation schemes which convey the common coil current to the individual outputs. This function works well under normal conditions, however, in case of an overload of the system, these schemes tend to affect the multiple outputs adversely.
Typically, conventional SIMO power converters comprise individual switching elements for each output, wherein said switching elements may form part of a switching matrix 12, as can be seen e.g. in FIG. 1. Regular output matrix control schemes typically regulate on and off times of said switching elements in order to control the values of the required (average) output currents. However, in case of an overload at one output, the power converter may transfer the current of the energized coil completely to this overloaded output, and the voltages at the other outputs may drop down as well if they have an output load to deliver.